BiologyCBSE Class 11 · Cell Cycle and Cell Division

Mitosis: Stages, Cytokinesis and Significance

Updated 17 October 2026 · Fact-checked

Mitosis is equational division in which a parent cell divides into two daughter cells with the same chromosome number. After interphase (G1, S, G2) it proceeds through prophase, metaphase, anaphase and telophase, followed by cytokinesis. It gives growth, repair, replacement and asexual reproduction.

Understand Mitosis: Phases and Significance

Cell cycle. The sequence of events by which a cell duplicates its genome, synthesises its constituents and divides. In human cells, the cycle takes about 24 hours; in yeast about 90 minutes. Two phases: interphase (the long preparatory phase) and M phase (mitosis, the actual division).

G₁: cell grows, makes RNA and proteins; DNA is not replicated.
S: DNA replication; DNA amount doubles from 2C to 4C, but the chromosome number stays the same (46 in a human cell); in animal cells centrioles duplicate in the cytoplasm.
G₂: proteins for mitosis are synthesised; growth continues.
G₀ (quiescent stage): cells that do not divide further exit G₁ and remain metabolically active (heart cells).

Mitosis (karyokinesis). Equational division: the number of chromosomes in the parent and daughter cells is the same.

Prophase: chromatin condenses into chromosomes, each with two chromatids joined at the centromere; the mitotic spindle starts forming from centrosomes moving to opposite poles; nucleolus and nuclear envelope disappear. Golgi and ER are reduced. Lasts longest in mitosis.
Metaphase: nuclear envelope has disappeared; chromosomes are maximally condensed, easiest to count; spindle fibres attach to kinetochores on centromeres; chromosomes align on the equatorial plane (metaphase plate).
Anaphase: centromeres split and sister chromatids separate; each chromatid is now a chromosome and moves to opposite poles; the centromere leads, arms trail.
Telophase: chromosomes reach the poles, decondense, nuclear envelope reassembles around each set, nucleolus, Golgi and ER reform.

Cytokinesis. Division of the cytoplasm.

Animal cell: a furrow in the plasma membrane deepens and pinches the cell into two.
Plant cell: a cell plate forms at the centre and grows outward to meet the lateral walls, from the middle lamella; wall-building Golgi vesicles.
Sometimes karyokinesis is not followed by cytokinesis, giving multinucleate (syncytial) cells, e.g. liquid endosperm of coconut.

Significance. Growth of multicellular organisms; cell repair and replacement (cells of the upper layer of skin, gut lining, blood cells); maintenance of the nucleo-cytoplasmic ratio; asexual reproduction in many forms; genetic stability.

Chromosome and DNA tracking in a human cell (2n = 46). G₁: 46 chromosomes, 2C. After S: 46 chromosomes (92 chromatids), 4C. Metaphase: 46 (92 chromatids), 4C. Anaphase: 92 chromosomes in the dividing cell. Each daughter after telophase: 46 chromosomes, 2C.

Draw and label: metaphase and anaphase of mitosis in an animal cell: spindle fibres, centrioles, chromosomes at equator, chromatids at poles.

Mitosis: Phases and Significance: key facts

Interphase: G1 growth
S DNA replication
G2 preparation; Long phase
Mitosis: $P r o p ha se ∣ m e t a p ha se ∣ ana p ha se ∣ t e l o p ha se$; Then cytokinesis
Numbers in 2n = 46: $G 1 : 46, 2 C ∣ a f t er S : 46 (92 c h r o ma t i d s), 4 C ∣ ana p ha se : 92∣ d a ug h t er : 46, 2 C$; Chromosome tracking
Cytokinesis: Animal: furrow | Plant: cell plate; Cytoplasm division

G1	growth
S	DNA replication
G2	preparation

How to answer Mitosis: Phases and Significance questions

Questions give a cell number and ask for chromosome counts, or a description of a stage.

1Identify the stage from the chromosome behaviour.
2Track chromosome number and DNA content (C) separately.
3Remember that S doubles DNA, not chromosome number.
4At anaphase, chromatids become chromosomes, so count doubles temporarily.
5For cytokinesis, state animal versus plant mechanism.

Mitosis: Phases and Significance in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Healing a cut

Suppose a shallow cut on the skin heals in a few days and a new top layer forms.

Which division is responsible and what does it ensure about genetic content?

Try it first, then show the solutionSolution

Mitosis produces new skin cells from existing ones.
Each new cell receives the same chromosome number and DNA.
This keeps the repaired tissue genetically identical to the original.

Answer: Mitosis replaces cells with identical copies.

Memory hook: Repair needs copies, not changes.

Tricks to remember Mitosis: Phases and Significance

Short memory aids. Say each one aloud once, then use it on a question the same day.

PMAT
Prophase, Metaphase, Anaphase, Telophase.
Use it when: Order
Meta = middle
Metaphase: chromosomes in the middle.
Use it when: Metaphase
Ana = apart
Anaphase: apart.
Use it when: Anaphase

Mitosis: Phases and Significance: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: G1 S G2 · 2 marks · Very short answerBoard level

What happens to DNA content and chromosome number in S phase of a human cell?

Try it first, then show the solutionSolution

DNA doubles from 2C to 4C (1 mark).
Chromosome number remains 46 (1 mark).

Answer: DNA doubles; chromosome number same.

Example 2: Metaphase · 3 marks · Short answerBoard level

Why is metaphase the best stage to study chromosomes? What is the role of kinetochores?

Try it first, then show the solutionSolution

Chromosomes are maximally condensed and lie on the equator, so easy to count and study (1 mark).
Kinetochores on centromeres are attachment sites for spindle fibres (1 mark).
They help pull chromatids apart in the next stage (1 mark).

Answer: Condensed, aligned; kinetochores bind spindle fibres.

Example 3: Counting at stages · 4 marks · Short answerHarder board level

A human cell (2n = 46) enters mitosis. Give the number of chromosomes and chromatids at G1, after S, at metaphase, at anaphase (per cell), and in each daughter.

Try it first, then show the solutionSolution

G1: 46 chromosomes, 46 chromatids (1 mark).
After S and at metaphase: 46 chromosomes, 92 chromatids (1 mark).
Anaphase: 92 chromosomes (each separated chromatid counts as one) (1 mark).
Each daughter: 46 chromosomes (1 mark).

Answer: 46; 46 (92 chromatids); 92; 46.

Example 4: Cytokinesis comparison · 3 marks · Short answerHarder board level

Compare cytokinesis in animal and plant cells and name one case where karyokinesis is not followed by cytokinesis.

Try it first, then show the solutionSolution

Animal: cleavage furrow pinches the cell (1 mark).
Plant: cell plate forms from the centre outward from the middle lamella (1 mark).
Liquid endosperm of coconut is multinucleate with no cytokinesis (1 mark).

Answer: Furrow versus cell plate; syncytium in coconut endosperm.

Example 5: Colchicine · 5 marks · Long answerHOTS / competency

Suppose a drug prevents spindle fibre formation. Predict at which stage mitosis stops, what happens to chromosome number in the cell, and why such a cell fails to complete division.

Try it first, then show the solutionSolution

Chromosomes cannot attach to spindle fibres, so division stops at metaphase (1 mark).
Chromatids cannot be pulled apart (1 mark).
DNA has been replicated, so the cell contains double the usual set if it later re-forms a nucleus (1 mark).
Cytoplasm division may or may not occur, leading to a polyploid cell (1 mark).
Cell cannot complete mitosis normally; mitosis requires the spindle for separation (1 mark).

Answer: Arrest at metaphase; polyploid possible.

Where students lose marks in Mitosis: Phases and Significance

The slips examiners see most often, and what to write instead.

Mistake: Chromosomes double in S
Chromatid count confused.
Wrong working
92 chromosomes after S.
Right working
46 chromosomes (92 chromatids).
Do this: Chromatids, not chromosomes.
Usually costs: 1 mark.
Mistake: Nuclear envelope present at metaphase
Stage confusion.
Wrong working
Nucleus intact in metaphase.
Right working
Envelope has broken down.
Do this: Prophase end.
Usually costs: 1 mark.
Mistake: Cell plate in animals
Mechanism swapped.
Wrong working
Animal cells form cell plates.
Right working
Animal furrow; plant cell plate.
Do this: Plants plate.
Usually costs: 1 mark.

Exam tips

Track chromosome and DNA values separately.
Describe chromosomes in each stage precisely.
Name both furrow and cell plate.
State that mitosis is equational.

Practice questions on Mitosis: Phases and Significance

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
DNA replication occurs in
(a) G1 (b) S (c) G2 (d) M phase
Hint
Synthesis.
Answer
(b).
Q2 · 1 mark · Assertion-reasonHarder board level
Assertion (A): The number of chromosomes doubles in the S phase.
Reason (R): DNA content doubles in the S phase.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Chromatids not chromosomes.
Answer
(d).
Q3 · 2 marks · Very short answerHarder board level
A cell with 12 chromosomes divides by mitosis. Give the chromosome number and DNA amount (in C, taking G1 as 2C) in each daughter, and at G2.
Hint
Same as parent.
Answer
Each daughter has 12 chromosomes and 2C DNA. At G2 the cell has 12 chromosomes and 4C DNA.
Q4 · 4 marks · Case-basedHarder board level
Read and answer.
Suppose a root-tip squash shows P: chromosomes lined on the equator; Q: chromatids moving to opposite poles; R: nuclear envelope reforming.
(a) Name stages. (1)
(b) Which is best for counting chromosomes? (1)
(c) What separates at Q? (2)
Hint
Metaphase, anaphase, telophase.
Answer
(a) P metaphase, Q anaphase, R telophase. (b) P. (c) Sister chromatids separate after the centromeres split.
Q5 · 4 marks · Long answerHOTS / competency
Suppose a plant meristem has 500 cells in G1 (2n = 14). After one complete mitotic division of all cells, find the number of cells and total chromosomes in the tissue. Why does the total DNA content change between G1 and G2?
Hint
Compute and explain.
Answer
Cells = 500 x 2 = 1000; chromosomes = 1000 x 14 = 14,000 (before: 500 x 14 = 7000). DNA doubles in S, so total DNA in G2 is twice that in G1; mitosis then halves it per cell.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Longest phase of cell cycle?Show answer
Interphase.
2.What is G0?Show answer
Quiescent stage.
3.Where do spindle fibres attach?Show answer
Kinetochores.
4.Mitosis result?Show answer
Two identical daughter cells.
5.Which stage has maximum condensation?Show answer
Metaphase.
6.Cell cycle length in human?Show answer
About 24 hours.

Mitosis: Phases and Significance: frequently asked questions

What is mitosis?

Equational division giving two identical cells.

What happens in S phase?

DNA replication.

What is karyokinesis?

Division of the nucleus.

What is cytokinesis?

Division of the cytoplasm.

Why is mitosis important?

Growth, repair and asexual reproduction.